We grow a mix of over-wintered onions and traditional main-crop onions. The techniques and considerations are similar for both, so I refer you to my guide to growing bulbing onions for most details.

This short section just gives you some specific hints and tips relating to over-wintered onions and whether your should grow them.

What's special about over-wintered onions?

Varieties that are suitable for over-wintering are very hardy and to be honest that's the main thing that sets them apart. They have two other very desirable properties though, they tend not to go to seed in late spring and they start to bulb when the day length exceeds 14 hours, rather than 16 hours, which is normal for main-crop onions.

<aside> 💡 14 daylight hours happens about mid April, i.e a full month earlier than 16 hours for main-crop onions in mid May and that makes a big difference in when they mature

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The result of these three characteristics, is an early harvest of onions. How early? Well it depends on whether you want to wait until your onions have a large bulb, or whether you are happy with smaller bulbs. We don't care that much about bulb size so we usually start by harvesting our biggest salad onions, and using them in cooking, in April. We start harvesting our biggest over-wintered bulbing onions in May and finish harvesting some time in June, or even early July for later grown succession. By then of course we could be harvesting our biggest main-crop onions.

Is it worth growing them?

There are several reasons why it's worth growing them in my opinion:

  1. you want a reliable supply of bulbing onions in spring, because you don't buy onions from the shops
  2. you have space, with nothing else growing, that you won't need until early summer
  3. It’s a hedge against anything going wrong with your main crop onions, which might suffer from drought, disease or pests
  4. they are less likely to get onion fly
  5. there’s not many other things that you can plant in October (except other alliums and broad beans)

all of these are true for us. We don't buy onions from the shops, so the earlier we can get lovely new, fresh onions the better, they are always better than stored onions from the previous August!

We also have space, this might come free after we harvest the winter squash in October (the perfect planting time for seedlings) and we don't need the space until June for planting sweetcorn and winter squash again.

There are some risks though, if your plants grow too big, usually because of a mild autumn, they might well go to seed in late spring. We don't worry about this, because we either harvest them early and small, or we just remove the flower stalk and use them as normal, either fresh or frozen.

<aside> 💡 The biggest downside is the increased potential for disease, which might contaminate your onion bed, but because we don't intermix our main-crop and winter crop, I don't worry about this.

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Do over-wintered onions store?

Many people claim that over-wintered onions don't store and need to be used 'immediately'. We have found this to be true for red onions, but not for the white onions that we grow. We find that - Toughball especially - grown from seed stores exceptionally well, when harvested in June. Right now in fact - in mid December - we have about 100 left and we haven't lost a single one to rot/mould, however by the end of January they are starting to go a little soft.